Colored it at home, and then gone to a stylist to 'fix' it without telling them about your do-it-yourself attempt?

Colored your permed hair, or permed your colored hair?

Left a relaxer on too long?

Gone several months without a haircut?

These are just a few of the most common mistakes that can lead to a doctor visit or a trip to the salon for repair work. Top hairstylists say they see these frequent mistakes at their salons -- mistakes that can damage your hair and leave you in desperate need of an emergency fix in the stylist's chair. How can you avoid wreaking havoc on your hair? Here are some key dos and don’ts from a doctor and leading hair experts.

Don’t Get Overheated

Many women like to "blow out" their hair at home by straightening and styling it with a brush and blow dryer. But that direct heat can actually burn your hair, says George Gonzalez, owner of George - The Salon in Chicago and a former stylist for many of Oprah Winfrey’s celebrity guests. "People put the dryer directly against the hair because they think that’s the way to get it straight. Especially with a metal brush, that can do real damage. If it’s not too bad, you can repair the damage with conditioners, but once hair is too overstressed and chemically dried out from heat, there’s nothing to do but cut it and let new hair grow in."

Even if you think it takes too long to style your hair this way, pull the blow dryer a bit away from the brush and don’t let it touch the hair directly.

Flat irons can also overheat the hair, but Gonzalez notes that most women move flat irons through the hair, as opposed to holding them at one spot for awhile as they do with blow dryers. But take care with over-ironing as well.

In addition to burns from a blow dryer, you can also burn your hair or scalp with chemicals used in hair processing. That’s a common problem, says Andrew Alexis, MD, MPH, who directs the Skin of Color Center at St. Luke’s - Roosevelt Hospital in New York City. “I often see chemical relaxers left on too long, to the point of burning or irritation of the scalp.”

He advises patients to have chemical processing applied by a trained professional who takes appropriate care to avoid injury to the scalp or excessive hair damage. Alexis suggests protecting the scalp with a petrolatum-based ointment, like petroleum jelly, that is applied before the relaxer, a step called “basing the scalp.”

Chemically treating hair and then exposing it to high heat -- for example, from a curling iron -- inflicts a double whammy of damage, says Alexis. “The hair is already weakened by the relaxer, and then damaged further by the intense heat exposure. This can cause hair to break very easily. With this in mind, I advise my patients to minimize the intensity and frequency of thermal hair styling techniques and to use conditioning shampoos to protect-strengthen the hair.” Alexis says that hair loss from traction alopecia and scalp burns due to chemical relaxers would usually be temporary, but if the damage is longstanding or severe enough, it can be permanent.

Be Realistic

Know what your hair can and can’t do. If you have very curly hair, it will need some layers -- but not too much, says Scott Buchanan, owner of Scott J Salons and Spas in New York and vice president of the Professional Beauty Association’s Salon/Spa Leadership Council. "If you layer the heck out of it, it will become too round," he says. "On the other hand, you do need to have some graduation or layers to let the curl form. If you leave it all one length, it just becomes a big pyramid frizz ball."

Be mindful of what hairstyle you’re willing to maintain. If you get your hair heavily colored, that means you’ll need to be back in the salon every few weeks. If you don’t have time for that, you’ll be walking around a lot of the time with half-grown roots. "You’ll look good for the first three weeks, and the next nine you’ll look awful," Buchanan says.

Don’t Go Solo With Color

For very simple highlighting or a color change that’s not too radical, maybe a home boxed hair color job will work out fine. But if you want significant or complex highlights, or want to go from ash brown to strawberry blonde, call in the experts.

"You can make a lot of mistakes with home coloring," says Rowena Yeager, who owns Studio Wish salon in Streetsboro, Ohio, and also serves on the PBA’s Salon/Spa Leadership Council. "Some of the worst results I’ve seen have been when someone has colored their hair and then attempted to correct it themselves as well. Often, people don’t realize that the color on the box is not necessarily the color their hair is going to be."

You also can’t "lift" one color with another color. In other words, if you colored your hair brown and now you’ve decided you want to go lighter, the color you get will only lighten the part of your hair that’s not already colored -- in other words, the roots. "You wind up with light roots and dark ends, which we call 'hot roots,'" says Yeager. "While it’s not damaging to your hair, it’s not particularly pretty. The only way to have that fixed is by a pro."

The same goes for perms, says Gonzalez. "Some women might get their hair permed -- either at home or in a salon -- and then not be happy with the results. So they go out and buy a relaxer at the drugstore." But using two different types of chemicals so close together can seriously damage the hair. "Once it’s chemically stressed, hair has no life to it and it’s impossible to style. It will just look dry and flat," Gonzalez says. So if you want a bad perm fixed, don’t do it yourself -- find another stylist.

Don’t Overcolor

You got your hair lightened for summer, and you really liked it. You liked it so much that you thought you’d go a little lighter. And then a little lighter still. "Every time you take a permanent color that’s lighter and pull it through somebody’s ends, you’re removing a lot of the natural oils and condition that’s already there," says Yeager. "Over time, the hair will get drier and drier, and lose its luster." As with heat-damaged hair, you may be able to fix some of the problem with oils and conditioners, but the only real remedy is to cut and grow out the straw-like strands.

Don't Overbraid

You may like tight braids or cornrows, but your hair and scalp may not. If you regularly wear your hair in this style, it can lead to a form of hair loss known as traction alopecia. “I treat many women, especially those of African descent, with thinning hairlines due to excessive tension from hairstyles associated with traction,” says Alexis.

Get Regular Trims

Yeager still remembers a friend she had in fourth grade, a girl with waist-length locks. The girl moved away, and then came back in sixth grade, with hair only halfway down her back. "You got your hair cut?" Yeager asked the girl. "No, Mom will never let me cut it," she replied.

Yeager realized that the girl’s hair had simply become so ridden with split ends that it had broken off on its own. "It was really tattered and torn and brittle-looking," she says. "Split ends are nature’s way of trimming. Especially as we get older and our hair has gone through years of blow drying, flat irons, curling irons, and wear and tear in the sun, we need regular trims. The maximum time between cuts should really be 8 weeks, especially if you blow dry and go out in the sun regularly."

Don’t Lie to Your Stylist

"People will come in to have their hair colored, and they won’t tell us that they’ve already tried coloring at home and been to two beauty salons," says Buchanan. "They keep trying to change their fabric -- hair is basically fabric. You can create what you want with it, but after awhile the fabric gets overworked, and you have to give it a break. We can’t help you if we don’t know what you’ve been doing to your hair."